At present, local back surface field batteries are an important research and development direction of efficient crystalline silicon solar batteries, and by means of a back surface passivation technique and a local back surface field structure, the recombination in the back surface of a solar battery can be remarkably reduced, the back reflection within long-wave bands is improved, and the absorption of free carriers in the back surface is reduced, such that the conversion efficiency of the battery is improved. At present, in order to reduce the process for preparing a back passivation battery, a back surface passivation film is locally opened using a laser or chemical slurry erosion method, then an aluminium layer is formed on the back surface using a silk screen printing or evaporation method, and then aluminium atoms instead of silicon atoms enter the silicon crystal lattice in a high temperature process to form a p-type heavily-doped region, i.e. a local back surface field, below the open film region.
However, when using a conventional method of full back surface printing or aluminium layer depositing, it is easy to form voids in the contact region in the high temperature process due to the difference of diffusion coefficients between aluminium and silicon, which causes: 1. a local back surface field cannot be formed, and severe recombinations in the back surface are caused; 2. the contact area between the local back surface field and the aluminium-silicon alloy layer becomes small, and the fill factor is reduced; and 3. due to the void effect, the thickness of the local back surface field is insufficient, and the formation of the voids restricts current local back surface field batteries, particularly the efficiency improvement of back point contact batteries.